Keep Track of Dull Cutter Edges

I use turning tools with carbide-insert cutters. The inserts can’t be sharpened, but the tools with square cutters have four edges, so you can rotate to a fresh edge when needed. Still, it can be hard to tell visually which edges are dull, so I just color the used edges on top of the insert with a permanent marker. Now it’s easy to keep track of how many sharp edges are still left before it’s time to replace the insert.